Pre-treatments and Leaching of Rare Earth Elements (REE) from Malaysian Bauxite

Abstract

The importance of rare earth elements (REE) in high-end technology applications has become increasingly notable. Malaysia is rich in mineral resources like bauxite ore, which contains a significant amount of REE. However, REE from bauxite cannot be extracted directly without pre-treatments and the growing concerns of environmental pollution, such as red dust and red mud, are partially due to the increased stockpile of bauxite residue (BR). The study intends to compare the effect of pre-treatments before the REE leaching process of the RB from Felda Bukit Goh, Kuantan, Pahang. The methods 1 (M1) and 2 (M2) included roasting, magnetic separation, Bayer process, acid cracking, leaching via (NH4)₂SO₄, and precipitation via C₂H₂O₄. In M2, lower current intensity in magnetic separation, a lower solid-to-liquid ratio and the absence of H₂O₂ in acid cracking were used. The RB contains light rare earth elements (LREE) between 190.20 to 318.71 mg/L with abundant cerium (Ce) and neodymium (Nd). The RB comprises of Fe₂O₃ 44.66%, Al₂O₃ 34.15%, TiO₂ 8.39% and SiO₂ 8.39% whereas gibbsite (Al(OH)₃) was the main mineral. In M1, the REE contents decreased by 12.5% (301.31 mg/L) and between 0.4% to 8.4% after roasting and magnetic separation, respectively. Via the Bayer process, REE contents increased by 15.5% (346.81 mg/L) in M1, whereas decreased by 48.4% (119.34 mg/L) in M2. In acid cracking using H₂SO₄ with H₂O₂ in M1, the REE contents majorly remained in BR, while without H₂O₂ the REE contents decreased, indicating REE has been leached out in M2. The H₂O₂ caused the BR to become viscous and harder after drying, leading to the REE interlocking in the residue. The overall leaching performances in M1 and M2 were achieved at 1.34% and 99.0%, respectively, evidently showing that introducing H₂O₂ before the leaching process does not improve the REE extraction. Meanwhile, precipitation via C₂H₂O₄, produced rare earth oxalate (REOx) up to 1.59 % in M1 and 31.80% in M2 where, based on element purity, the Ce and Nd in M2 attained were 92.78% and 7.20%, respectively.